CORRESPONDENCE
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Discoloration of Dextrose Solutions SIR: It is known that dextrose solutions become dark in color in the course of manufacture and processing. Thus, Fellers, Miller, and Onsdorff (1) made the following observations: The subject of dextrose sirups to high temperatures tends to darken them, though the color change is influenced to a large extent by the pH value of the solution. At pH 4.5 there is no serious change in dextrose when heated to l l O o C. ( 2 3 0 O F.)for 20 minutes. However, at 121O C . (249.8O F.) considerable darkening takes place. * * * Alkalies have a marked darkening effect on dextrose solutions although dilute acids are without effect. * * * Sweet corn containing dextrose became dark in color and was of poor flavor, no doubt because of the decomposition of the dextrose at the processing temperature of 121.1' C.
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tion was traced to a marked increase in the hydrogen-ion concentration with increase in the dextrose concentration. For example, the pH value of 0.04 N hydrochloric acid is 1.43, whereas the pH values of 20 and 40 per cent dextrose solutions in acid of this strength are 1.31 and 1123, respectively. 3. The colorof heated dextrose solutionsvarieswith the p~ value of the solution and, as shown by Figure 1, reaches a minimum value in the p H range 2.3 to 3.0. The position of the minimum is not affected by the oxygen of the atmosphere. 4. Heavy metals-for example, iron and copper-do not noticeably influence the color developed when acid dextrose solutions are heated a t 130' C. Salts of trivalent iron form complex
manufacture and processing of dextrose solutions become obvious. As far as possible the p H value of the solution should be kept in the neighborhood of 2.3 to 3.0. Furthermore, the lowest feasible concentration and temperature should be maintained. On the other hand, the maintenance of these ideal conditions in practice is a difficult problem. It is often impossible, as in the preserving industry, to keep the dextrose solution within the most favorable pH range. Furthermore, as was pointed out by Fellers, Miller, and Onsdorff, a lowering of the dextrose concentration is cer-
